Containers for liquids are periodically drained for a variety of reasons. If the container is air tight, provisions should be made for allowing air to enter the container. The air displaces the liquid and enables the liquid to more readily drain. Fuel filter/water separators used in vehicle fuel systems must periodically be drained to purge contaminants which accumulate therein. In many types of fuel filter/water separators, air must be introduced into the body of the unit before the contaminants may be drained.
To enable draining air tight containers, several types of self venting drain valves have been previously developed. These self venting drain valves are generally mounted at or near the bottom of the container. These valves introduce air into the container through an inlet while allowing the fuel and/or contaminants to drain through a fluid outlet in the valve. In some designs, such as the one shown in U.S. Pat. No. 4,724,074, the air inlet is located in close proximity to the fluid outlet of the valve. In such designs it is usually necessary to prime the fluid outlet of the valve in advance of the air inlet vent being opened. Priming the fluid outlet creates a slight vacuum inside the unit. Thereafter, when the air vent is opened, only air will be drawn in through the vent. This avoids liquid flowing outward through the vent as well as air being drawn into the unit through the liquid outlet opening. Either of these conditions would impede draining of the unit.
Self venting drain valves of the type previously known to Applicant have been constructed in two ways. The most common type of self venting drain valve uses a threaded knob which is accepted into the underside of the fluid container. The knob contains two integral passageways. From a closed position, the knob is rotated several turns which causes it to move outward due to the interaction of the threads. Eventually, a liquid passageway is opened through the knob to the interior of the fluid container. The opening of the liquid passageway primes the outlet of the drain valve. Further rotation of the knob additional turns, opens an air passageway which vents the container and enables air to displace the liquid which flows outward through the liquid outlet of the valve. This type of self venting drain though generally satisfactory, presents certain disadvantages. First, it requires the use of mating threads on the knob and on the container. It also requires two separate seals and sealing surfaces. These features add to manufacturing cost and each is a potential source of leakage or failure of the valve.
Another type of self venting drain valve construction employs a threaded drain knob and a spring loaded vent. As the knob is turned several rotations a fluid outlet is opened. Further outward movement of the knob opens a spring loaded vent allowing air to enter the interior of the container. Such construction is shown in U.S. Pat. No. 4,855,041 which is owned by the assignee of the present invention. Again, this type of drain valve construction has the associated expense and potential problems of threaded pieces and multiple seals.
Both types of conventional self venting drain valves have an additional drawback that the drain knob must be turned multiple turns to reach an opened condition. This takes time. Also, the knobs typically have no stops to prevent them from being over tightened when closed, or from being loosened too far to a point where the knob disengages the threads and falls off the container.
Another type of prior art drain valve shown in U.S. Pat. No. 4,753,266 has a body member that extends into the container to be drained and a rotatable valve member disposed outboard thereof. The valve member is turned in a threaded guide to bring fluid outlet and air inlet openings in the body and valve members into alignment to vent and drain the container. The body is configured so that the opening for the vent is at a higher vertical elevation in the container than the opening for the fluid. This ensures that air goes in and fluid comes out the proper openings. This valve design must provide means for sealing of the threaded rotable valve member and for sealing the body member to the container into which it extends. Both of the seals present areas of possible failure.
Other problems with conventional self venting drain valves are that they extend substantially beyond the lower wall of the unit or container on which they are mounted. This increases the probability that the drain valve may be inadvertently bumped open or completely knocked off the unit. Another problem is that it is sometimes desireable to connect a hose to the drain valve to carry away the fluid discharged from the container. This is not easily done to a drain valve which requires several turns to be opened.
Thus there exists a need for a self venting drain valve that is simpler and less expensive to manufacture. There further exists a need for a self venting drain valve that is lower in profile, opens quickly and which may be readily attached to a hose.